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United States Patent |
6,266,202
|
Nguyen
,   et al.
|
July 24, 2001
|
Closed loop write verification in a disc drive
Abstract
An apparatus and method for performing real-time, closed loop write
verification in a disc drive having a rotatable magnetic disc and a head
having read and write elements. During a write operation, the disc drive
generates a write current signal indicative of input data to be written to
the disc. The write current signal is applied to the write element, which
generates a time-varying magnetic field to simultaneously induce a
readback signal in the read element through magnetic coupling of the read
element to the write element, and to magnetize the disc to write the input
data to the disc. The readback signal induced in the read element is used
to reconstruct a set of output data which is used to verify accuracy of
the input data.
Inventors:
|
Nguyen; Hieu V. (Oklahoma City, OK);
Dakroub; Housan (Oklahoma City, OK)
|
Assignee:
|
Seagate Technology LLC (Scotts Valley, CA)
|
Appl. No.:
|
326070 |
Filed:
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June 4, 1999 |
Current U.S. Class: |
360/53; 360/31; 360/46 |
Intern'l Class: |
G11B 005/09; G11B 027/36 |
Field of Search: |
360/31,46,53
|
References Cited
U.S. Patent Documents
3810236 | May., 1974 | Horowitz et al.
| |
4599717 | Jul., 1986 | Bracht et al.
| |
5255270 | Oct., 1993 | Yanai et al.
| |
5289478 | Feb., 1994 | Barlow et al.
| |
5422760 | Jun., 1995 | Abbott et al.
| |
5471351 | Nov., 1995 | Ishiguro.
| |
5475665 | Dec., 1995 | Tani et al.
| |
5532992 | Jul., 1996 | Funamoto.
| |
5717673 | Feb., 1998 | Ohkubo.
| |
6111708 | Aug., 2000 | Jewell et al. | 360/31.
|
Primary Examiner: Neal; Regina Y.
Attorney, Agent or Firm: Crowe & Dunlevy
Parent Case Text
RELATED APPLICATIONS
This application claims priority to U. S. Provisional Application No.
60/088,169 filed Jun. 5, 1998.
Claims
What is claimed is:
1. In a disc drive having a rotatable magnetic disc and a head having a
read element and a write element, a method for writing data to the disc
comprising steps of:
(a) generating a write current signal indicative of the data to be written
to the disc;
(b) applying the write current signal to the write element to generate a
time-varying magnetic field, wherein the magnetic field simultaneously
induces a readback signal in the read element through magnetic coupling of
the read element to the write element, and magnetizes the disc to write
the data to the disc; and
(c) using the simultaneously induced readback signal to verify accuracy of
the data written to the disc.
2. The method of claim 1, further comprising steps of:
(d) subsequently transducing the data written to the disc during the
applying step (b) to generate a second readback signal; and
(e) using the second readback signal to verify accuracy of the data written
to the disc.
3. The method of claim 1, wherein the using step (c) comprises steps of:
(c1) reconstructing a series of data symbols and associated code symbols
from the readback signal; and
(c2) using the code symbols to detect and correct erroneous data symbols.
4. The method of claim 1, wherein the data to be written to the disc are
characterized as an input set of data, wherein the generating step (a)
comprises passing the input set of data into a buffer, and wherein the
using step (c) comprises steps of:
(c1) recovering an output set of data from the readback signal;
(c2) placing the output set of data in the buffer; and
(c3) comparing the output set of data to the input set of data.
5. A method for verifying data written to a disc drive having a
controllably positionable head adjacent a rotatable disc with a magnetic
recording surface, the head having a write element which selectively
magnetizes the recording surface to write data to the disc and a read
element which transduces the selective magnetization of the recording
surface to read data from the disc, the method comprising steps of:
(a) magnetically coupling the read and write elements so that passage of
write currents through the write element generates a time-varying magnetic
field which simultaneously induces a corresponding readback signal in the
read element and selectively magnetizes the recording surface;
(b) writing data to the recording surface; and
(c) verifying accuracy of the writing step (b) using a readback signal
induced in the read element during the writing step (b).
6. The method of claim 5, further comprising steps of:
(d) subsequently transducing the data written to the disc during the
writing step (b) to generate a second readback signal; and
(e) using the second readback signal to verify the accuracy of the writing
step (b).
7. A disc drive, comprising:
a rotatable disc having a magnetic recording surface;
a read/write head controllably positionable adjacent the recording surface
and having a write element and a read element, the read element
magnetically coupled to the write element;
a write driver which applies a series of write currents to the write
element to write an input set of data to the disc, the write element
generating a time-varying magnetic field in response to the write
currents; and
a read channel which recovers an output set of data from a readback signal
simultaneously induced in the read element as the input set of data is
written to the disc.
8. The disc drive of claim 7, wherein the disc drive uses the output set of
data to verify accuracy of the first set of data.
9. The disc drive of claim 7, wherein the write element writes the input
set of data to a selected data block of the disc, wherein the readback
signal is characterized as a first readback signal and the output set of
data is characterized as a first output set of data, and wherein the read
channel subsequently recovers a second output set of data from a second
readback signal obtained as the read element transduces the selective
magnetization of the selected data block.
10. The disc drive of claim 7, wherein the read channel comprises a partial
response, maximum likelihood data path for normal readback operations in
parallel with a peak-detect data path used for on-the-fly write
verification detection operations.
11. The disc drive of claim 7, wherein the read channel comprises a single
partial response, maximum likelihood data path which switches between two
different sets of channel parameters, with one set used during normal
readback operations and the other set used during on-the-fly write
verification detection operations.
12. A disc drive, comprising:
a rotatable disc; and
means for writing a set of data to the disc and for simultaneously
verifying accuracy of the set of data written to the disc without
transducing the set of data from the disc.
Description
FIELD OF THE INVENTION
The present invention relates generally to the field of disc drive devices
and more particularly, but without limitation, to performing real-time,
closed loop write verification through magnetic coupling of read and write
elements of a disc drive head.
BACKGROUND OF THE INVENTION
Disc drives are used as primary data storage devices in modern computers
and computer networks. A typical disc drive includes a head-disc assembly
(HDA) housing one or more magnetic discs which are rotated by a spindle
motor at a constant high speed and accessed by an array of read/write
heads which store data on tracks defined on the disc surfaces. Electronics
used to control the operation of the HDA are provided on a printed wiring
assembly ("circuit board") which is mounted to the underside of the HDA.
Each head is typically provided with separate read and write elements, with
a common configuration utilizing a thin film, inductive write element and
a magneto-resistive (MR) read element. Data are written by passing a write
current through the write element, with the write current generating a
time-varying magnetic field which selectively magnetizes the disc surface.
Previously written data are read using the read element to transduce the
selective magnetization of the disc to generate a readback signal which is
used by a read channel to reconstruct the data. An interface circuit
buffers and controls the transfer of data between the disc and a host
computer.
Technological advancements in the art have resulted in continued
improvements in disc drive data storage capacities and transfer rates. It
has not been at all uncommon for each successive generation of drives to
provide substantially twice the data storage capacity as the previous
generation, at an equal or improved data transfer rate. Design cycle times
are also being shrunk to the point that a new generation of drives is
typically introduced into the marketplace every few months.
The commercial success of disc drives is not only a result of the
costeffective manner in which vast amounts of user data can be stored and
retrieved, but also in the demonstrated reliability of the typical disc
drive over a relatively long operational life. Nevertheless, for
applications where data integrity is critical, methodologies have been
developed to further enhance the ability of disc drives to consistently
and accurately store and retrieve data.
One such methodology is the grouping of a plurality of drives into a
multi-drive array, sometimes referred to as a RAID ("Redundant Array of
Inexpensive Discs"). Since their introduction, RAIDs have found widespread
use in a variety of applications requiring significant levels of data
transfer, capacity and integrity performance. Various RAID architectures
employ mirroring (simultaneously writing data to two or more identical
drives), striping (writing portions of the data across multiple drives)
and interleaving (employing various types of error detection and
correction schemes at multiple levels to ensure data integrity).
Another particularly useful methodology to maximize data integrity is
through the use of write verification, which involves the writing of data
to a disc followed by a subsequent read operation where the previously
stored data are retrieved from the disc to ensure the data were correctly
written. However, such write verification operations undesirably decrease
the data transfer performance of the disc drive, as each write operation
requires each sector to which data are written to be accessed at least
twice: first, when the data are written, and second, when the data are
subsequently read back for verification. Conventional write verification
techniques accordingly impose a severe penalty on disc drive performance,
limiting data transfer rates to levels substantially below that which
would be otherwise achievable.
As consumer demands continue to drive further advances in data transfer
rate and integrity performance, there remains a continual need for
improvements in the disc drive art whereby these often mutually exclusive
characteristics can be optimized. It is to such improvements that the
present invention is directed.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and method for performing
closed-loop, real time write verification in a disc drive.
In accordance with a preferred embodiment, the disc drive has a rotatable
magnetic disc, and a head with read and write elements with the read
element being magnetically coupled to the write element.
Data are written to the disc by first generating a write current signal
indicative of the data to be written and then applying the write current
signal to the write element. In response, the write element generates a
time-varying magnetic field which magnetizes the disc to write the data to
the disc, while simultaneously inducing a readback signal in the read
element as a result of the magnetic coupling of the read element to the
write element. The readback signal is used to verify the accuracy of the
writing operation.
More particularly, a set of output data is reconstructed from the readback
signal and compared to the data originally written to the disc. In this
manner, the data written to the disc can be verified on-the-fly,
eliminating the need for a subsequent read operation to verify the data.
The write verification can be performed during substantially all write
operations, or on a sampled basis as a diagnostic tool or error recovery
routine. One read channel configuration includes the use of a single
partial response, maximum likelihood (PRML) data path that switches
between two different sets of channel parameters, with one set used during
normal readback operations and the other set used during on-the-fly write
verification. An alternative read channel configuration employs a PRML
data path for normal readback operations in parallel with a peak-detect
data path used for write verification detection.
These and various features as well as advantages which characterize the
present invention will be apparent from a reading of the following
detailed description and a review of the associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 provides a top plan view of a disc drive constructed in accordance
with preferred embodiments of the present invention.
FIG. 2 is an generalized representation of the construction and operation
of read and write elements of a selected head of the disc drive of FIG. 1.
FIG. 3 illustrates the general manner in which data are stored on each disc
of the disc drive of FIG. 1.
FIG. 4 provides a representation of the format of each servo field of FIG.
3.
FIG. 5 provides a representation of the format of each data field of FIG.
3.
FIG. 6 is a functional block diagram of the control electronics of the disc
drive of FIG. 1.
FIG. 7 is a WRITE VERIFICATION routine, illustrative of steps preferably
carried out by the disc drive of FIG. 1 to perform closed-loop write
verification in accordance with a preferred embodiment of the present
invention.
FIG. 8 provides graphical representations of write current, normal readback
and magnetically-coupled readback signal curves.
FIG. 9 illustrates one preferred read channel configuration which employs a
partial response, maximum likelihood (PRML) data path for normal readback
operations in parallel with a peak-detect data path used for on-the-fly
write verification detection operations.
FIG. 10 illustrates an alternative read channel configuration which
includes the use of a single PRML data path that switches between two
different sets of channel parameters, with one set used during normal
readback operations and the other set used during on-the-fly write
verification detection operations.
DETAILED DESCRIPTION
The present discussion will now turn to a detailed description of various
preferred embodiments of the claimed invention. Referring first to FIG. 1,
shown therein is a top plan view of a disc drive 100 used to store and
retrieve computerized data.
The disc drive 100 includes a head-disc assembly (HDA) 101 and a disc drive
printed wiring assembly (PWA) which is mounted to the underside of the HDA
101 and thus, not visible in FIG. 1. As discussed below, the PWA provides
circuitry necessary to control the operation of the HDA 101 and to
transfer data between the HDA 101 and a host computer in which the disc
drive 100 can be mounted in a user environment.
The HDA 101 includes a base deck 102 to which various disc drive components
are mounted. A top cover, which has been omitted from FIG. 1 to facilitate
the present discussion, cooperates with the base deck 102 to form an
internal, sealed environment for the disc drive 100. A spindle motor 104
is provided to rotate a stack of discs 106 at a constant high speed, with
a disc clamp 108 securing the discs to the spindle motor 104.
To access the discs 106, a controllably positionable actuator assembly 110
is provided which rotates about a cartridge bearing assembly 112 in
response to currents applied to a coil (a portion of which is shown at
113) of a voice coil motor (VCM) 114. The actuator assembly 110 includes a
plurality of arms from which corresponding flexure assemblies extend, the
topmost of which are identified at 116 and 118, respectively. Heads 120
are provided at distal ends of the flexure assemblies 116, 118 and are
supported over the discs 106 by air bearings established by air currents
set up by the rotation of the discs 106.
A latch assembly 122 is provided to secure the heads 120 over texturized
landing zones (indicated by broken line 123) at the innermost diameters of
the discs 106 when the disc drive 100 is deactivated. A flex circuit
assembly 124 provides electrical communication paths between the actuator
assembly 110 and the disc drive PWA.
Referring to FIG. 2, each of the heads 120 includes a thin-film inductive
write element 132 and a magneto-resistive (MR) read element 134. The write
element 132 writes data to the corresponding disc 106 by generating a
timevarying magnetic field (indicated generally at 136) across a gap 138
in response to write currents applied to the write element 132. The
magnetic field 136 operates to selectively magnetize the disc 106 along a
direction of movement of the disc 106 (as indicated by arrow 140).
Magnetic flux transitions result at locations where reversals in the
magnetization of the disc occur, such as shown at 142.
The read element 134, preferably disposed in the write gap 138 of the write
element 132, is characterized as providing a changed electrical resistance
in the presence of a magnetic field of selected orientation. Hence, by
passing a bias current through the read element 134, previously stored
data can be transduced from the magnetized disc surface and converted to a
readback signal in relation to changes in the voltage across the read
element. As discussed below, the disc drive 100 further operates to
perform real-time, closed loop write verification by using the read
element 134 to detect the time-varying magnetic field 136 from the write
element 132 during a write operation.
At this point, however, it will be useful to briefly discuss the general
manner in which data are arranged on the tracks. FIG. 3 shows a portion of
a track 150 on a selected disc 106, with each track including a number of
periodically disposed servo blocks 152 which are written to the discs
during manufacturing. The servo blocks are used to control the radial
position of the heads and are radially aligned to extend from an innermost
radius to an outermost radius of the disc, much like spokes of a wheel.
Between each successive pair of servo blocks are a number of data blocks
154 (sectors), which are used to store user data and are generated during
a disc drive formatting operation. The general formats of the servo blocks
152 and the data blocks 154 are set forth by FIGS. 4 and 5.
As shown in FIG. 4, an automatic gain control (AGC) field 156 stores an
oscillating pattern (such as a 2T pattern) to prepare servo control
circuitry (not shown in FIG. 4) of the disc drive for receipt of remaining
portions of the servo field 152. A synchronization (sync) field 158
provides timing information to the servo control circuitry. Index and Gray
code fields 160, 162 respectively, indicate angular and radial position of
the servo field 152. A position field 164 provides inter-track positioning
information.
FIG. 5 shows AGC and sync fields 166, 168 respectively, which prepare read
channel circuitry (not shown in FIG. 5) for receipt of user data which are
stored in a user data field 170. Error correction code (ECC) words,
appended to the user data to facilitate error detection and correction,
are stored in ECC field 172.
FIG. 6 provides a generalized functional block diagram of the control
electronics arranged on the aforementioned disc drive PWA in accordance
with preferred embodiments of the present invention. It will be noted that
arrowed paths are provided between respective functional blocks to
indicate the general interconnection thereof.
A selected head is denoted at 120, with corresponding write and read
elements 132, 134. It is contemplated that the write and read elements 132
and 134 are magnetically coupled, as shown; that is, the head is
constructed so that the read element 134 is subjected to the time-varying
magnetic field 136 generated by the write element 132 during a write
operation. While the placement of the read element 134 within the gap 138
of the write element 132 (as shown in FIG. 2) represents one preferred
construction, such placement is not necessarily required to achieve the
desired operation of the disc drive 100.
Continuing with FIG. 6, a preamplifier/driver circuit ("preamp/driver") is
set forth at 174 and includes a write driver 176 and a read preamp 178,
with the write driver 176 applying write currents to the write element 132
and the read preamp 178 applying a read bias current to the read element
134. Additional circuitry, such as head selection logic and a bias current
source, have been omitted from FIG. 6 for purposes of clarity. For
reference, the preamp/driver 174 is preferably mounted to the actuator
assembly 110 within the confines of the HDA 101 (FIG. 1), to minimize the
physical distance separating the head 120 and the preamp/driver 174.
A communication channel 180 is operably coupled to the preamp/driver 174,
and includes a write channel 182 which encodes and serializes input user
data for writing by the write driver 176, and a read channel 186 which
receives readback signals from the read preamp 178 and reconstructs
previously stored user data therefrom. It will be noted that alternative
preferred constructions for the read channel 186 will be discussed below.
Continuing with FIG. 6, data from the servo blocks (152, FIGS. 3 and 4) are
passed from the read channel 184 to a servo circuit 186, which includes a
programmable digital signal processor (DSP) 187 to carry out head
positioning operations. An interface circuit 188 has a buffer 190 to
temporarily store data during data transfer operations between the discs
106 and a host computer (not shown). The storage capacity of the buffer
190 preferably comprises several megabytes (MB). Transfers between the
buffer 190 and discs 106 are controlled by a disc interface 192, and
transfers between the buffer 190 and the host computer are controlled by a
host interface 194. A processor interface 196 enables communication
between the interface circuit 188 and a system processor 198, which
controls overall operation of the disc drive 100. For a more detailed
discussion of the construction and operation of a typical interface
circuit, see U.S. Pat. No. 5,262,662 issued to Shaver et al., assigned to
the assignee of the present invention.
FIG. 7 provides a flow chart for a WRITE VERIFICATION routine 200,
illustrative of steps carried out by the disc drive 100 in accordance with
a preferred embodiment to perform closed-loop write verification of data
written to the discs 106. During a write operation, the first set of data
to be written is selected, as shown by step 202. While the amount of data
in the first set of data can vary depending on the application, preferably
the first set of data represents an amount that can be accommodated by the
user data field 170 of a selected data block 154 (FIG. 5), such as 512
kilobytes (kB). Of course, a large user file is typically broken down and
written to a number of data blocks 154, with the file being transferred to
the buffer 190 and incrementally outputted to the write channel 182.
The write channel 182 operates to encode and serialize the data (denoted as
"D1") to enable the write driver 176 to generate write currents indicative
of the data D1, as shown by step 204. This operation includes run-length
limited (RLL) and error correction code (ECC) encoding, to facilitate
subsequent retrieval of the recorded data.
The write currents generated at step 204 are applied to the write element
132 to generate the time-varying magnetic field necessary to write the
data D1 to the corresponding data field 154, step 206. Simultaneously, as
shown by step 208, the read element 134 detects the time-varying magnetic
field from the write element 132, due to the magnetic coupling between the
read element 134 and the write element 132, and outputs a readback signal
in response thereto.
It will be noted that the readback signal is generated in response to the
magnetic field from the write element 132 and not from the selective
magnetization of the disc 106. In this regard, the read element 134
"senses" the operation of the write element 132 in real time, unlike
conventional write verification schemes where the read element 134
subsequently transduces previously written data from the disc 106. To
achieve this real time sensing, a read bias current is applied to the MR
read element 134 during the writing of data by the write element 132.
After preamplification by the read preamp 178, the readback signal is
reconstructed by the read channel to generate a set of readback data
("D2"), as indicated by step 210. A comparison between the readback data
D2 and the written data D1 is next performed at decision step 212. This
comparison can be achieved in a number of ways. In one preferred
embodiment, a direct comparison is made. More particularly, the initially
written set of data (D1) is retained in a portion of the buffer 190, so
that once the reconstructed set of data (D2) is recovered to the buffer
190, the two sets of data can be compared.
In another preferred embodiment, error correction codes (ECC) can be
employed in the reconstructed set of data to determine whether any errors
are detected in the reconstructed data D2. It will be noted that the use
of ECC allows different levels of data integrity assurance, in that ECC
allows detection and correction up to a selected number of errors in the
readback data. Hence, the acceptability of a write verification operation
(i.e., the operation of decision step 212) can be based on the ability of
the disc drive 100 to recover the data D2, regardless of the number of
erroneous bytes of data detected and then corrected by ECC; alternatively,
although the disc drive 100 successfully recovers all of the data D2, in
particularly critical data integrity applications an excessive number of
detected errors might result in the data being further evaluated for a
possible rewriting operation.
Continuing with FIG. 7, when the recovered data D2 does not match the
written data D1 (or is otherwise deemed sufficiently marginal), the
associated data block 154 is marked for subsequent evaluation, step 214.
Such marking is typically achieved using a status register which indicates
the status of the various data blocks of the disc drive 100. The routine
next determines whether additional sets of data remain to be written,
decision step 216; if so, the next set of data is selected at step 218 and
the routine returns as shown.
When all of the data have been written, the routine continues to decision
step 218, which determines whether any of the accessed data blocks have
been marked for further evaluation. If so, the first such marked data
block is selected at step 220 and a conventional read verification
operation is performed, step 222. That is, the read element 134 is
positioned over the associated data block to transduce the selective
magnetization of the user data field 170 (and ECC field 172) to generate a
readback signal which is presented to the read channel 184 for
reconstruction. If any uncorrected errors are detected in the recovered
data, decision step 224, error recovery routines are applied at step 226
in an attempt to recover the data. Such routines can involve adjustment of
various read channel and preamp/driver parameters, application of a
position offset to move the read element 134 away a selected distance from
the center of the track, etc. A general discussion of such routines is
provided in U.S. Pat. No. 5,721,816 issued to Kusbel et al., assigned to
the assignee of the present invention.
Continuing with the routine of FIG. 7, a determination is next made whether
the operation of step 226 was successful (i.e., whether uncorrectable
errors remain), as indicated by decision step 228. If so, the data block
is marked for a rewrite operation at step 230. The routine continues to
decision step 232 to determine whether additional data blocks have been
marked for evaluation; if so, the next marked data block is selected at
step 234 and the routine continues as shown. Finally, the routine ends at
step 236.
It will be noted that various alternatives can be readily implemented based
on the flow of FIG. 7. For example, for purposes of enhancing data
integrity it may be desirable to rewrite data blocks that exhibit
uncorrected errors (step 224), regardless whether the disc drive 100 can
subsequently recover such errors during step 226. Maintaining the data to
be written in the buffer 190 during the entire operation of the routine
would facilitate efficient rewriting of any deficient data blocks.
Successfully performing the routine for all of the data blocks on a single
track before moving to a different track would also result in certain
efficiencies of operation.
It will further be noted that, although the foregoing discussion generally
contemplates full-time simultaneous write verification, the write
verification routine of FIG. 7 can also be performed on a sampled basis,
depending upon the requirements of the user. For example, the routine can
be implemented as part of an error recovery routine, so that the routine
is performed in response to an error detected during a conventional write
operation. Because the write verification presented above advantageously
operates to detect a failed electrical interconnection path between the
preamp/driver 174, the routine can also be used as a self-diagnostic
routine periodically performed at appropriate times during drive
operation, such as during idle times when the discs 106 are still
spinning, but no host commands are being serviced.
Various alternative configurations for the read channel 184 will now be
discussed with reference to FIGS. 8-10. FIG. 8 shows graphical
representations of a write current signal curve 240, a normal readback
signal curve 242 and a coupled readback signal curve 244, each being
plotted against a common x-axis 246 indicative of elapsed time and a
common y-axis 248 indicative of respective signal amplitudes.
The write current signal curve 240 provides a general representation of
pulsed write currents that are applied by the write driver 176 (FIG. 6) to
the write element 132 (FIGS. 2, 6) to selectively magnetize the associated
disc 106. As discussed above, transitions in current polarity (indicated
at 250) in the write current signal curve 240 generate the magnetic flux
transitions 142 on the disc surface (FIG. 2).
The normal readback signal curve 242 is generally indicative of the
readback signal generated during a conventional read operation as the MR
read element 134 transduces the flux transitions 142 from the disc
surface. The characteristics of a given normal readback signal such as 242
will depend on a number of factors, including the construction of the
drive, the presence of electrical noise, the position of the head, etc.
Hence, the curve 242 has been presented to generally illustrate a typical
readback response, with positive and negative amplitude peaks 252
resulting from the detection of the flux transitions 142 on the disc
surface.
The coupled readback signal curve 244 generally represents the readback
signal that is induced in the MR read element 134 as a result of the
magnetic-coupling between the write element 132 with the read element 134,
as discussed above. For clarity, it will be noted that the coupled
readback signal curve 244 and the normal readback signal curve 242 are not
generated at the same time; that is, the coupled curve 244 is generated
simultaneously during a write operation as the write current signal 240 is
being applied to the write element 132, whereas the normal curve 242 is
generated later during a subsequent, conventional read operation at a time
when no write current is applied to the write element 132.
The coupled readback signal curve 244 has positive and negative peaks 254
which are generated in response to the transitions 250 of the write
current signal curve 240. The peaks 254 are generally better defined than
the peaks 252, due to the relatively large energy content of the write
current signal curve 240 necessary to realign the magnetic orientation of
the disc surface to store data. It is contemplated that the amplitudes of
the peaks 254 will typically be substantially greater than the amplitudes
of the peaks 252, although this is not reflected in FIG. 8, as the
amplitudes of the curves 240, 242 and 244 have been normalized for ease of
illustration.
With this review of the general differences between normal readback signals
and coupled readback signals that will typically occur, reference is now
made to FIG. 9 which illustrates one preferred configuration for the read
channel 184 of FIG. 6. More particularly, FIG. 9 employs a partial
response, maximum likelihood (PRML) data path 260 in parallel with a
peak-detect write verify data path 262.
The PRML data path 260 is configured to receive the normal readback signal
curve 242 (FIG. 8) and use PRML signal processing techniques to
reconstruct the user data therefrom in a conventional manner. The
peak-detect data path 262 is configured to receive the coupled readback
signal curve 244 (FIG. 8) and to use appropriate threshold levels to
detect the peaks 254 in order to reconstruct the write verify data set
from the write current signal curve 240. An advantage of the configuration
of the circuit of FIG. 9 is the relative ease in which a conventional
peak-detection circuit can be incorporated into an existing PRML signal
processing integrated circuit and utilized as desired while minimizing
disturbance to the configuration of the PRML readback path.
An alternative configuration for the read channel 184 is set forth by FIG.
10, which employs a single PRML data path that is used for both normal
readback operations and on-the-fly write verification detection
operations. PRML channel constructions are well known and can take a
number of forms, such as exemplified in U.S. Pat. No. 5,422,760 issued to
Abbott et al. Nevertheless, to facilitate the present discussion, a brief
overview of selected portions of the PRML data path will be presented.
The PRML data path set illustrated in FIG. 10 includes an automatic gain
control (AGC) block 270 which applies variable gain amplification to
normalize the peak-to-peak signal amplitude of the input readback signals
from the read preamp 178. An adaptive prefilter 272 provides frequency
domain filtering. A finite impulse response (FIR) filter 274 (also
referred to as a "transversal equalizer") filters the signal to a selected
class of partial response filtering. A slicer 276 samples (digitizes) the
signal and a Viterbi detector 278 recovers the data bit sequence
therefrom. A decoder 280 removes RLL encoding from the sequence and
performs other related functions to allow the data to be passed to the
buffer 190 of the interface circuit 188 (FIG. 6) for further processing.
During operation in accordance with the embodiment of FIG. 10, a first set
of adaptive parameters are utilized by the read channel 184 for the normal
readback signal curve 242 (FIG. 8) to decode the user data transduced from
the disc surfaces. Such adaptive parameters can be used to adjust gain
levels of the AGC 270, filtering characteristics of the prefilter 272, tap
weights used by the FIR 274, etc. and can be supplied, for example, by the
system processor 198 (FIG. 6).
Additionally, when the above discussed on-the-fly write verification
detection operations are desired, a second set of adaptive parameters can
be readily loaded into the various circuits of FIG. 10 to enable recovery
of the data content of the coupled readback signal curve 244 of FIG. 8. An
advantage of this approach is that little or no additional circuitry may
be required in the PRML read channel, provided that sufficient parametric
adaptability and processing overhead are available to effect the switching
between the two parameter sets.
It will now be appreciated that the claimed invention, as illustrated by
the various embodiments presented above, facilitates improved data
transfer rates by reducing the need for a subsequent read operation to
verify written data. In summary, during a write operation a write current
signal is generated (step 204) indicative of input data to be written to
the disc. The write current signal is applied to a write element 132,
which generates a time-varying magnetic field 136 to simultaneously induce
a readback signal in a read element 134 through magnetic coupling of the
read element to the write element, and to magnetize a disc 106 to write
the input data to the disc (steps 206, 208). The readback signal induced
in the read element is used to reconstruct a set of output data (step 210)
which is used to verify accuracy of the input data (step 212). For
purposes of the appended claims, the recited "means for writing a set of
data to the disc and for simultaneously verifying accuracy of the set of
data written to the disc without transducing the set of data from the
disc" will be understood consistent with the foregoing discussion to
correspond to the disclosed MR head 120 having separate write and read
elements 132, 134 which are magnetically coupled to each other; the preamp
174 configured to simultaneously apply write currents to the write element
and read bias current to the read element; a communication channel 180
with a read channel 184 and write channel 182; and interface circuit 188.
It will be noted that prior art structures that perform write verification
by subsequent reading from the media (disc) do not perform the recited
function, and are further expressly excluded from the definition of an
equivalent. Prior art structures that fail to have separate read and write
elements in the head and instead use the same element to write and
subsequently read data are incapable of performing the invention and are
thus also expressly excluded from the definition of an equivalent.
It will be clear that the present invention is well adapted to attain the
ends and advantages mentioned as well as those inherent therein. While a
presently preferred embodiment has been described for purposes of this
disclosure, numerous changes may be made which will readily suggest
themselves to those skilled in the art and which are encompassed in the
spirit of the invention disclosed and as defined in the appended claims.
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